Key Takeaways from the FBI’s Switch to 9mm

Guest Post by Ryan Cardone

Ryan Cardone is a Nashville-based writer in the outdoor, survival and tactical niches. When he isn’t at the gym or playing chess, he can be found doing research for his next article.

The caliber debate has probably existed since the time of bows and arrows. With 9mm, .40 S&W and .45 ACP all having established track records in military and law enforcement, none of these calibers could be considered a bad choice. But for those who want to optimize what they have at their disposal to the greatest degree possible, is there a case for one that is preferable?

A Document of Interest

In 2014, a letter written by the FBI Academy Training Division in Quantico, VA and addressed to law enforcement partner agencies was released via FOIA request. The document gave a summary justification for why the agency had recently switched to handguns chambered for 9mm Luger for their standard issue pistols and why they recommended the same for law enforcement partners.

The document is a summary and not necessarily meant to be a final word on all caliber debates. But for those intrigued, it represents some of the best information publicly available on the topic. The FBI is fairly well-heeled and has the budget and capabilities to conduct extensive testing that goes well beyond the anecdotal evidence and conjecture many caliber conversations are composed of. This post examines some of the key takeaways in the document that could benefit the reader’s understanding and preparedness.

Background Context

For those who have followed the topic for a while, the 9mm justification letter is particularly interesting given the FBI’s history with the caliber. In 1986, the agency catalyzed a movement away from 9mm to .40 S&W after the famous Miami shootout left investigators wondering whether lives could have been saved had special agents been armed with more firepower.

The conclusion after the shootout was that agents needed to carry semi-autos chambered with something more lethal. A few years later, the .40 S&W was born and became a law enforcement staple.

So, what changed to make the FBI switch to 9mm in recent years?

Key Point from the Letter: Projectile vs Caliber

The letter has several sections that cover the realities of projectile performance, terminal ballistics, medical factors (penetration and cavity), psychology and tactics. It gives a handful of citations (which is a handful more than most caliber conversations) and appears to be well-researched as far as an executive summary goes.

The author starts off by pointing out that projectile, not caliber, should be the main focus of the conversation. This is a surprisingly good point that seems rarely discussed in debates. Today, dramatically different types of projectiles exist, and it stands to reason they exhibit respectively different performance qualities. Caliber, on the other hand, refers to the diameter of the projectile and is a secondary quality which does not necessarily dictate performance.

Terminal Ballistics

With this in view, specific factors that relate to performance are cavitation and penetration, whether in regards to the body or environmental barriers. The document squarely identifies shot placement as the determining factor for incapacitation and emphatically dismisses the concept of stopping power as mythological. It also points out that the difference in permanent cavities from varying handgun projectiles is almost indiscernibly small even to forensic investigators. As for temporary cavities (the short-lived tissue flexing that results from the pressure wave generated by the projectile), the document dismisses them as an insignificant factor that provides no meaningful wounding or incapacitating properties.

Instead, the focus falls on the tactical realities of penetration (with a preference for 12″ – 18″), the accuracy of shot strings and capacity. While 18″ may sound like a lot, considering varying conditions of cover and clothing, irregular bullet paths and suboptimal angles of entry, this seems to be a good metric for achieving the projectile’s purpose effectively. From an agency perspective, it also touts the cost benefits of 9mm not only in terms of lower ammunition prices but also less wear and tear on weapons over time. The document’s author concludes that modern premium 9mm projectiles have an equal if not better performance when compared to their .40 and .45 caliber peers.

Tactical Considerations

The FBI found shooters capable of better accuracy in multiple shot strings when handling the generally lower recoil 9mm. This brings us to one of the most shocking and oft-quoted quotes of the document: “LEO’s [sic] miss between 70 – 80 percent of the shots fired during a shooting incident”

This assertion tells us two things:

1. Even the FBI is not above the grammatical error known as the grocer’s apostrophe.
2. LEOs land a shockingly low number of rounds on target.

The letter gives no citation for the astounding claim and one could theoretically question the variety of contexts that might lead to such a statistic (e.g. extended shootouts would reasonably weigh the average much higher towards misses when lumped together with more common close individual encounters). Nevertheless, it does give a very real reason to opt for more capacity whenever possible.

And while anyone could speculate they could outshoot the average LEO, even with twice the aforementioned hit rate one would be doing well to land three or four rounds on target before emptying a fully loaded 1911.

With 9mm holding several benefits over larger calibers, among them cost, capacity and achievable accuracy within multiple shot strings, the obvious reason for carrying .40 or .45 would be increased terminal effectiveness (as defined by the projectile’s speed at neutralizing an adversary; lethality isn’t a good measure as non-survivable wounds can still leave an opponent with minutes to continue violent action).

But vital organ disruption, rapid blood loss or central nervous system deactivation must occur to immediately stop a determined opponent. For those less determined, the psychosomatic effects of being shot may be enough to cause them to retreat or fall down irrespective of the projectile or shot placement.

If modern premium 9mm projectiles can do this equally well as their slightly larger peers, yielding the same terminal effectiveness with none of the drawbacks of .40 and .45, then why not go 9mm?


And such is the argument of the FBI document. While not everyone may consider this conclusion final, it presents a strong case that today’s top-performing 9mm projectiles show no discernable disadvantages in man-stopping performance when compared to their counterparts.

That said, with the US military still honoring an international precedent of refraining from using expanding ammunition, certain agencies may still see the advantages .40 and .45 can offer in hardball form. And it should be remembered that law enforcement may not always have the most premium ammunition available from their departments. Considering limitations like these, there are circumstances where the advantage could still shift in favor of the larger calibers.

And of course, with established track records and effective deployment in countless professional contexts .40 and .45 can never be considered poor choices altogether. However, the FBI 9mm Justification letter gives a fascinating and well-constructed case for why one may opt for 9mm if given the choice. For those for whom capacity and affordability are major factors, the document suggests that you may enjoy these benefits of 9mm without the need to worry about missing out on performance.

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